The invention relates generally to the area of open web steel framing and concrete floor buildings and more particularly to a primary steel framing member, in the form of a truss, in which the top chord acts as the shear connector in a composite system.
Composite design has been used in the construction industry for many years. The development and sophistication of economic structural systems gradually extended to steel buildings and concrete floor construction, the result of which was to significantly reduce cost of steel framing in the industry. However, composite construction was confined to primary wide flange or solid section members with stud-type shear connectors welded onto the top flanges in the field, and secondary framing members such as joists or beams, but not to primary trusses.
As those skilled in the industry are aware, conventional composite design consists essentially of three elements; that is, concrete, a steel beam or joist and a shear transfer mechanism. In the past, the shear transfer mechanism has usually been a stud shear-connector welded to the top flange of the beam and then the stud was encased in the concrete. Obviously, the shear-connecting device or stud, properly welded to the top flange of the beam, must be capable of developing the necessary shear force between the stud on the beam and the concrete to produce the desired composite action.
It will be appreciated that the purposes of composite floor construction are to save considerable steel weight and cost, as well as to reduce vibration and deflection. Concrete conventionally has not been intrinsically tied to the upper chord of a truss and thus the entire vertical primary member loading is taken by the steel truss alone. As stated above, it was for this reason that stud-type shear connectors were welded to the upper chord of a steel girder or beam, but shop-applied studs are costly and hazardous and generally objected to or rejected by labor unions and disallowed by safety regulations for those reasons. While composite construction has been used with joists, as evidenced in some of the patents identified below, the composite theory has not as stated above, been applied to trusses.
Among the prior-art patents which are considered to be of interest with respect to the instant invention are several which are owned by Hambro Structural Systems Ltd. of Ottawa, Canada. Those patent numbers are: U.S. Pat. Nos. 3,913,296; 3,845,594; 3,841,597; 3,979,868; and 3,818,083. The patents just cited are directed to secondary member composite floor construction as opposed to the instant invention in which a primary open-web framing member is one of the elements in a composite floor construction.